Method of producing controlled displacement of screen elements in cathode ray tubes



- Aug. 30, 1-960 F. .1. BINGLEY 2,950,969

METHOD OF PRODUCING CONTROLLED DISPLACEMENT OF SCREEN ELEMENTS INCATHODE RAY TUBES Filed Feb. 27, 1957 2 Sheets-Sheet 1 IN VEN TOR.FK/i/VA J BIA/61 E) Aug. 30, 1960 F. J. BINGLEY METHOD OF PRODUCINGCONTROLLED DISPLACEMENT OF SCREEN ELEMENTS IN CATHODE RAY TUBES FiledFeb. 27, 1957 2 Sheets-Sheet 2 IN VEN TOR.

nited States Patent,

METHOD OF PRODUCING CONTROLLED DIS PLACEMENT OF SCREEN ELEMENTS IN CATH-ODE RAY TUBES Frank J. Bingley, Meadowbrook, Pa., assignor to PhilcoCorporation, Philadelphia, Pa., a corporation of Pennsylvania Filed Feb.27, 19 57, Ser. No. 642,848

3 Claims. (Cl. 96-41) This invention relates to the manufacture ofcathode ray tubes and more particularly to the production of controlleddisplacement of screen elements in such tubes. The invention furtherrelates to a method of producing a sub-master for use in the manufactureof cathode ray tubes wherein it is desired to effect controlleddisplacement of screen elements according to a predetermined pattern.

While not limited thereto, the invention is particularly applicable tothe manufacture of color image-producing cathode ray tubes to be used incolor television receivers employing a single cathode ray tube. Thescreen of such a tube has groups of elements thereon emissive of lightof different colors, and it also has index elements for producing anindexing signal which is utilized to effect proper coordination betweenmodulation and position of the image-producing beam, such coordinationbeing requisite for proper color rendition. The cathode ray tube screenpreferably comprises 7 parallel phosphor stripes arranged in colortriplets, each triplet comprising three phosphor stripes which respondto electron impingement to produce light of three primary colors such asred, green and blue. The index elements preferably are in the form ofspaced stripes and they are positionally related to said triplets. .Thenumber of index elements may be equal to, greater or less than thenumber of groups of colored light-emissive elements.

In any cathode ray tube employing index elements, the electronimpingement on said elements causes a flow of energy from each point ofimpingement to a common output point from which the indexing signal isderived and is fed to an external circuit. The flow of energy may besecondary electron emission, light emission, conductive flow ofelectrons, or of any other character. Thus, the index elements may becomposed of a material, such as magnesium oxide, to emit secondaryelectrons to be collected by a collector electrode: or they may becomposed of a material, such as zinc oxide, to emit light to be receivedby photo-electric means; or they may be composed of conductive materialand may be connected to a common output lead.

In a co-pending application of R. G. Clapp, Serial No. 634,217, filedJanuary 15, 1957, Patent No. 2,899,581, there is disclosed and claimed ascreen structure wherein the index elements and the groups of coloredlight-emissive elements are relatively displaced to eliminate orminimize color error. Asset forth in the Clapp application, the colorerror is due to time variation between the electron impingement on theindex elements and the performance of the aforementioned coordinatingfunction, and according to the Clapp invention the screen elements arerelatively displaced as a function of said time variation over thescreen area. While it is possible to displace either the coloredlight-emissive elements or the index elements, it is usually simpler todisplace the index elements.

In the preferred method of'manufacture of a cathode ray tube of the typehere involved, as described in a copending application of M. Sadowsky etal., Serial No. 408,219, filed February 4, 1954, Patent No. 2,870,010,each set of screen elements is formed by first applying to the screen acoating of photosensitive material, then exposing to light the portionsof the coating where the elements are to be provided, then applying thematerial which is to form the elements and finally Washing away theunexposed portions of the coating. In such method, the selectiveexposure of stripe portions to light is accomplished by projecting lightthrough a master having spaced transparent stripes but being otherwiseopaque.

In a co-pending application of J. B. Chatten, Serial No. 641,934, filedFebruary 25, 1957, there is disclosed and claimed a method whichprovides zone-by-zone displacement of screen elements of a cathode raytube. Thus, with respect to color error in a color image-producing tubeof the character above-mentioned, the Chatten method may be employed toprovide zone-b-y-zone displacement generally in accordance with thepredetermined color error pattern. In accordance with the preferred formof that method, a sub-master is produced by successively exposingdifferent zones or areas of a photographic plate to light through amaster in such a manner as to effect zone-by-zone displacement of themaster image on said plate. Then the plate is developed and it becomes asub-master having the desired pattern of displacement, and it is used toexpose to light those portions of the cathode ray tube screen where thedisplaced ele ments are to be formed.

In producing the sub-master, the preferred procedure is to first make amap of the screen area zoned according to the different degrees ofdisplacement desired in the various zones. Thus, where the objective isto eliminate or minimize color error in a color image-producing cathoderay tube, the map is zoned according to the degrees of color error. Thenzone plates or masks are made according to the zoning of the map, andthe masks are used in conjunction with the aforementioned'master inmaking the desired sub-master.

With the foregoing in mind, the principal object of the presentinvention is to provide an improvement ofthe Chatten method. w v r .Inaccordance with this invention, onlytwo precisely- .formed zone masksare made regardless of'the number of zones, one of which zone masks isthe exactconverse or negative of the other, and roughly-formedmaskscorresponding in number to. the number of zones are made for use withthe precisely-formed zone-masks. The precisely-formed masks serveaccurately to define theborders of the various zones, and theroughly-formed masks serve in cooperation With the precisely-formedmasks-to define the zones in succession- The masks are utilized inassociation with a master to produce a pattern of the variouspositioning of the screen elements in the zones successively defined bythe masks. 1 a I The invention may be fully understood from'thefollowing detailed description with reference to the accompanyingdrawings, wherein: W

Fig. 1 illustrates, by way of example, a pattern of displacement ofindex elements in a cathode ray tube;

Fig. 2 shows a set of masks employed according to the present invention;I

Fig. 3 is a perspective view showing how the displacement pattern isproduced; and r Fig. 4 is a face view of a sub-master produced accordingto the preferred form of this invention.

It will be understood that the displacement of the index elements iswith reference to a normal position representing zero displacement. Incolor television receivers in which the color-representative signalsuccessively represents the primary colors red, green and blue, thepreviously mentioned color triplets of the cathode ray tube each maycomprise three phosphor stripes emissive of light of the said colors inthe order mentioned. Suppose that there is one index stripe for eachcolor triplet and that the normal position of the index stripes isdirectly behind the red light-emissive stripes. Then if the space ordistance between consecutive red light-emissive stripes is regarded as360 electrical degrees, and if each red lightemissive stripe is regardedas positionally representing zero displacement, each greenlight-emissive stripe may positionally represent 120 displacement, andeach blue light-emissive stripe may positionally represent 240displacement. "Thus if an index stripe were displaced 120, it would beshifted from its normal position to a position directly behind the greenlight-emissive stripe.

Referring first to Fig. 1, there is illustrated a pattern ofdisplacement of the index stripes which has been found to be suitable tocompensate for varying transit time of secondary electrons in a cathoderay tube employing index elements emissive of secondary electrons. Inthis illustration, the area of the cathode ray tube screen which isvisible to a viewer is represented as defined by the border line 10. Thescreen area is represented ash is seen by a viewer. The screen area isdivided into zones wherein the displacement of the index stripes to theright'increases zone-by-zone in 5 increments. Thus within the centralzone, the index stripes have zero displacement; within the immediatelyadjacent zone, the index stripes have 5 displacement; within the nextzone the index stripes have displacement; and so on.

It will be realized that it is impossible to illustrate to scale theactual displacements which are very small. By way of example, two of theindex stripes are shown at 11 and 12 with the displacement greatlyexaggerated so as to be clearly visible. Since the index stripe 11extends through the central zone, it has zero displacement within thatzone, but in the other zones through which it extends, it is displacedto the right the number of degrees represented by each zone. Since theindex stripe 12 does not extend through the central zone, it isdisplaced to the right in all of the zones through which it extends, thedisplacement in each zone being the number of degrees represented bythat zone. 1

In the preferred practice of this invention, a map of the screen area isfirst made, with contour lines thereon as in Fig. 1, dividing the areainto zones according to the desired pattern of displacement of the indexstripes. Then the aforementioned masks are made according to the zonepattern of the map, and these masks are used in conjunction with astriped master to produce the desired pattern of displacement of theindex stripes.

The method according to this invention may be clearly understood byconsidering it with reference to a simple pattern. Suppose, for example,that the screen area is divided into four simple zones-a central zone,two concentric annular zones, and an outer zone. According to thisinvention, two precisely-formed zone masks are made, as shown in Fig. 2at 13 and 14, and four roughly-formed masks are made, as shown at 15 to18.

The manner in whichthese masks are used to produce the desired patternof displacement of the index stripes is simply illustrated in Fig. 3. Inthe preferred practice of the invention, a photographic plate 19 issubjected to successive exposures by employing the masks in conjunctionwith a striped mask or master 20. The latter has opaque stripes 21 andis otherwise transparent. It may consist of a photographic plate whichhas been selectively exposed and developed. The spacing of the opaquestripes 21 corresponds to the desired spacing of the index stripes onthe screen of the cathoderay tube.

Light from a point source 22 passes through the master and through twoof the masks, and produces an image on a ground glass plate 23. Thisimage is projected through a lens 24 onto the photographic plate 19. The

projected image is displaced for each exposure of the photographicplate, preferably ;by displacement of the 28 free to transmit light.

master 20, although this could be accomplished in other ways, as bydisplacing the photographic plate or the lens or the light source.

Referring again to Fig. 2, the first precisely-formed zone mask 13 hasaccurately defined transparent zones 25 and 26, and is otherwise opaque.The second precisely-formed zone mask 14 is the exact converse ornegative of mask 13, and it has accurately defined transparent zones 27and 28, being opaque in the areas corresponding to the transparent zones25 and 26 of mask 13. An important advantage of thismethod is that thetwo precisely-formedmasks may be made from a common mother plate bycontact printing followed by ordinary development-of one mask plate andreversal development of the other mask plate. This insures that theglass supporting base will be on the same side of the gelatin emulsionin both masks, which is important because of the refraction of theglass.

The first roughly-formed mask 15 is to be used with mask 13 and its solepurpose is to cover the transparent zone 26 while leaving thetransparent zone 25 free to transmit light. Accordingly, mask 15 has atransparent area 29 and is otherwise opaque. Obviously, the size of thetransparent area 29 may vary within the limits imposed by thetransparent zones 25 and 26 of mask 13. Therefore, the mask 15 mayberoughly-formed for its intended purpose stated above.

The second roughly-formed mask 16 is intended to be used with the zonemask 14, and its sole purpose is to cover the transparent zone 28 whileleaving the transparent zone 27 free to transmit light. Accordingly,mask 16 has a transparent area 30, and it is otherwise opaque.

It will be seen that the size of the transparent area 30 may vary wtihinthe limits imposed by zones 27 and 28 of mask 14, and therefore, themask 16 may be roughlyformed for its intended purpose above indicated.

The third roughly-formed mask 17 is intended to be used with mask 13,and its sole purpose is to cover the transparent zone 25 while leavingthe transparent zone 26 free to transmit light. Accordingly, mask 17 hasan opaque area 31 and is otherwise transparent. Obviously, the size ofthe opaque area 31 may vary within the limits imposed by the transparentzones 25 and 26, and therefore, the mask 17-may be roughly formed.

The fourth roughly-formed mask 18 is intended to be used with the zonemask 14, and its sole purpose is to cover transparent zone 27 whileleaving transparent zone Accordingly, mask 18 has an opaque area 32andis otherwise transparent. Obviously, the size of the opaque area 32 mayvary within the limits imposed by the transparent zones 27 and 28, andtherefore the mask 18 may be roughly formed.

Referring again to Fig. 3 and considering in detail the sequence ofoperations involving the masks of Fig. 2, the master 20 is initially ina position corresponding to zero displacement of the index stripes. Themasks 13 and 15 are first placed between master 20'and the ground glassplate 23. Then the point source of light 22 is turned on. It will beseen that the central area 33 of photographic plate19 will be exposedexcept for stripes 34 which will remain unexposed.

The light source is then turned ofiand the masks 13 and 15 are replacedby masks 14 and 16. The master 20 preferably is moved slightly to theright a distance corresponding to the index displacement desired in thezone defined by the transparent area 28 of mask 14. The light source 22is then turned on, exposing the next area of plate 19 except for stripesslightly offset in relation to the stripes 34.

The same procedure is followed with the masks 13 and.

17, and with the masks. 14 and 18, with the master 20 slightly displacedfurther to the right in each instance to effect the desired indexdisplacement.

In this process, ;it,is important that the precisely-formed masks beprecisely positioned since their .purposeis to stripe portions of thescreen.

i define accurately the borders of the successive zones. On the otherhand, the roughly-formed masks need notbe precisely positioned sincethey merely serve to cover or tn'as'k portions of the precisely-formedmasks. In practice, the process may be carried out by means of aprojector having provision for precise location of the pre cisely-formedmasks and also having provision for precise displacement of the master.It will be realized, of course, that Fig. 3 is intended to illustrateclearly the method involved and is not intended to represent actualdispositions of the elements.

As a result of this process, the photographic plate 19, afterdevelopment, has transparent stripes as shown in Fig. 4 and is otherwiseopaque. At its central portion, the plate 19 has the transparent stripes34 which have zero displacement. The next zone of the plate 19 hastransparent stripes 35 which are slightly displaced to the right. Thenext zone of the plate 19 has transparent stripes 36 which are furtherslightly displaced to the right. The outermost zone on the plate 19 hastransparent stripes 37 which are still further slightly displaced to theright.

As previously mentioned, the preferred method of manufacture of acathode ray tube of the type here involved is that described in theaforementioned Sadowsky et a1. application. The index stripes areprovided on the screen of the cathode ray tube according to said method,using the plate or sub-master 19 to expose to light stripe portions ofthe screen corresponding to the stripes 34 to 37 in Fig. 4. Thus theindex stripes are provided on the screen according to the pattern of thetransparent stripes of sub-master 19.

While in practice the pattern of displacement of the index stripes, suchas shown in Fig. 1, involves a much greater number of zones than thesimple displacement pattern of Fig. 4, it will be understood that theproduction of a sub-master having the displacement pattern of Fig. 1simply requires a greater number of roughlyfortned masks, in addition tothe two zone masks, and a greater number of successive exposures of thephotographic plate which is to constitute the sub-master. In the case ofa pattern such as shown in Fig. 1, each of the roughly-formed masks fromthe third one on will have an opening or transparent area through whicha particular zone may be exposed. The last several masks will haveopenings or transparent areas for exposure of the similar corner zones.

It will be apparent that this method is applicable no matter how manyzones there are in the desired pattern. In any case, one of theprecisely-formed zone masks is transparent in the odd-numbered Zones,while the other precisely-formed zone mask is transparent in theevennumbered zones. Of course, the roughly-formed masks correspond innumber to the total number of different zones, as their puropse is toexpose the zones in succession when employed in conjunction with thezone masks, as described above with reference to Fig. 2.

-As above described, in the preferred practice of this invention thedisplacement pattern of the screen elements is produced on a sub-masterwhich is then used to produce the same pattern on the screen of acathode ray tube. Once the sub-master is produced it can be used toproduce the pattern on screens of successive cathode ray tubes.

It will be apparent, however, that the displacement pattern could beproduced directly on the screen of a cathode ray tube by this method.Thus in Fig. 3, instead of successive exposure of zones of the plate 19,a photosensitive coating on the screen of a cathode ray tube could beexposed zone-by-zone, utilizing a striped master having transparentstripe portions so as to expose However, this procedure would betime-consuming and expensive because each cathode ray tube would requirethe multiple exposure process.

gara es 6 From the foregoing description, it will be'seen that themethod according to this invention comprisesproducing a pair of zonemasks, one havingtransparent zones corresponding to the odd-numberedzones of the screen area, and the other having transparent zones cor:responding to the even-numbered zones ofthe screen area, producing othermasks successively cooperable wi-th said zone masks alternately todefine in succession zones corresponding to the zones of the screenarea, and utiliz ing said masks in association with a master toproduce'a pattern according to the desired positioning of screenelements in the successive zones of the screenarea.

This method has the advantage that, regardless of the number of zonesinto which the screen area is divided, only two precisely-formed zonemasks are required and these may be made from a common mother plate ashereinbefore described. 7

The roughly-formed masks may be cheaply made from any opaque material.Thus in the array of Fig. 2, the masks 15 and 16 could consist of opaquepaperwith holes cu t therein, and the masks 17 and 18 could consist ofopaque paper disks. It should be noted, however, that if glass is used,it should be of the best grade to avoid diiferences of refraction.

While the invention has been described with reference to specific formsand applications, it is to be understood that the invention is notlimited thereto but contemplates such modifications and otherapplications as may be resorted to by those skilled in the art.

I claim:

1. In the manufacture of color image-reproducing cathode ray tubeshaving colored light-emissive elements and index elements on the screenthereof, wherein an index signal is produced by flow of energy fromsuccessively scanned points of the screen area to a common output point,and wherein for proper color rendition it is desired that saidlight-emissive elements and said index elements shall have differentpredetermined relative positions in predetermined successive zones ofthe screen area,

a method of establishing desired difierent positioning of elements insaid zones which comprises producing a pair of precisely-formed zonemasks, one having transparent zones corresponding precisely to alternateones of said zones and being otherwise opaque, and the other being anexact negative of the first mask, said masks being adapted to be usedalternately, producing other masks which when placed individually and insuccession adjacent to the alternately-used zone masks serve incooperation with the latter to define in succession transparent zonescorresponding respectively to the successive zones of the screen area,ar ranging a photosensitive surface for exposure from a light source,interposing said zone masks alternately and said other masks insuccession between said surface and said light source to define forexposure successive zones of said surface corresponding respectively tothe successive zones of the screen area, and at the same time projectingthrough said masks onto the successively-defined zones of said surfaceimages of the screen elements according to the desired dififerentpositioning of said elements in the successive zones of the screen area,and finally developing said v stripes according to the desired patternof the index stripes over the screen area, which comprises making a mapof the screen area with lines on the map dividing it into the saidsuccessive zones, producing according to said map 7 a pa n xs sel -femed one masks, on a n t n nar tzqne cp tssn ndin p q s lt 1tmet 9ns saidand be n herwise o a ue n h ethe being an exact negative of the firstmask, said masks being adapted to be used alternately, producingaccording to said map other masks which when placed individually and insuccession adjacent to the alternatelyused zone masksserve incooperation with the latter to define iii-succession transparent zonescorresponding respectiyely to the successive mapped zones of said screenarea, arranging a photographic plate for exposure from a light source,inte posing said zone masks alternately and said other masks insuccession between said plate and said light source to define forexposure successive zones of said plate corresponding respectivelyto thesuccessive mapped zones ofsaid screen area, and at the same timeprojecting through said masks onto the successiveiy-de fined zones ofsaid plate images of the index stripes according to the desireddifferent positioning of the index stripes in the different zones ofsaid screen area, and finally developing said plate so that it hastransparent stripes ac- References Cited in the file of this patentUNITED STATES PATENTS 853,072 Morikoa Apr. l2, 1 932 2,462,150 WilkinsonFeb. 22, 1949 2,617,337 Snyder NOV. 11, 1952 Tondreau et al Sept. 8 1953OTHER REFERENCES Clerc Photography, Theory & Practice, page 342,Greenwood & Co. Ltd., 1937, London; Clerc Photography, Theory &Practice, page 99,-Green: wood & Co. Ltd, 1937, London. i H

1. IN THE MANUFACTURE OF COLOR IMAGE-REPRODUCING CATHODE RAY TUBESHAVING COLORED LIGHT-EMISSIVE ELEMENTS AND INDEX ELEMENTS ON THE SCREENTHEREOF, WHEREIN AN INDEX SIGNAL IS PRODUCED BY FLOW OF ENERGY FROMSUCCESSIVELY SCANNED POINTS OF THE SCREEN AREA TO A COMMON OUTPUT POINT,AND WHEREIN FOR PROPER COLOR RENDITION ITIS DESIRED THAT SAIDLIGHT-EMISSIVE ELEMENTS, AND SAIS INDEX ELEMENTS SHALL HAVE DIFFERENTPREDETERMINED RELATIVE POSITIONS IN PREDETERMINED SUCCESSIVE ZONE OF THESCREEN AREA, A METHOD OF ESTABLISHED DESIRED DIFFERENT POSITIONING OFELEMENTS IN SAID ZONES WHICH COMPRISES PRODUCING A PAIR OFPRECISELY-FORMED ZONE MASKS, ONE HAVING TRANSPARENT ZONES CORRESPONDINGPRECISELY TO ALTERNATE ONES OF SAID ZONES AND BEING OTHERWISE OPAQUE,AND THE OTHER BEING AN EXACT NEGATIVE OF THE FIRST MASK, SAID MASK BEINGADAPTED TO BE USED ALTERNATELY, PRODUCING OTHER MASKS WHICH WHEN